Extractive fractionation process



April 17, 1951 L. c. FETTl-:RLY 2,549,372

ExTRAcTIvE FRAc'rIoNATIoN PRocEss Filed April 15, 1947 f/rff ff/Amref ,mfr/Aff g Mmm/,afar

Patented Apr. 17, 1951 UNITED lSTA'IES PATENT DFFIC 2,549,372 EXTRAGTIVE FRACTIONATION PR01-)Ess 'Llqydjd Fettrly, Lengpeach, Calif., assigner to Shell Developl'nent` Company, San Francisco, Calif'., a corporation of Delaware- ApplicationApril- V1-"5, 1947, Serial No.'- 741,676

7 Claims; (Cl. 26T-666) This invention relates to a process' forv the ex' tractive fractionation of organi compounds'. More particularly, it relates to improvements 'in the process of fractonally electingorg'anic conpounds from mixtures thereof by the use of such complex-forming agents as urea and thiourea.

The fractionation of mixtures of organic compounds presents complex problems, both technica] and economic. For example, the separation of mixtures of closely allied. isomers, such as octane from iso-octane, is difficult by any of the more reasonably economic procedures, such as fractional distillation. Further, efficiency of conversion procedures such as alkylation, isomerization and cyclization is reduced if fed stocks are not of the correct composition,y either during the primary feed state o-r in recycling operations.

VInv'most of such conversion reactions an equi- -librium mixture is generally obtained'comprising -ixedratios of unconverted feed stock and the desired product. -If the feed. stock initially con tains some of. the conversion preduct, such as from a previous cycle through the converter,- the amount'of conversion is correspondingly reduced.

The two principal means for fractionation of such mixtures ona commercial scale have been by fractional distillation and by solvent extraction? f Recently, however, a new method has been shown to be suitable for large scale separations, namely extractive crystallizationnwith urea. It was found thaturea forms crystallinecomplexes with organic compounds of substantially straight chain structure, While it appears to be inert in this respect toward branched compounds such as the isoparafns, or cyclic compounds such as most aromatics and naphthenes. The complexes so formed are of indeterminate structure, but appear to be unstable molecular complexes rather than true chemical reaction products. This is indicated by their unstable character and the consequent ease of the regeneration of their components, namely urea and the unaltered organic compound.

When thiourea is the complex-forming agent employed the complexes formed therebyare usually of`a substantially different character in that thiorea forms complexes With organic' cmpounds having either a branched configuration or a cycloaliphatic structure. Under normaloperating conditionsthiourea forms only minor amounts of complexes With organic compounds of Straight chain Stllctll, Such as the nofl'al parans, Mixtures of 'these complex-forming agents have been employed 'to' extract' normal and' branched non-aromatic compounds as Well as naphthe'nes -rom mixtures containing other t'yes o'mpounds usually in excess. This latter process is usually employed for the purification of aromatics such as benzene, toluene, etc. K

These processes are particularly applicable to the refinement of petroleum or other hydrocar bon mixtures, especially those of unbranched structure (which may be suitably fractionated by complex formation With urea) or hydrocarbons of branched chain or saturated cyclic structure lwhich readily form complexes with thiourea). The general procedure knownto the prior ar't comprised` treatment of such mixtures WithV a solution of the complex-forming agent. Under these circumstances a mixture of complexes usually vlas formed. This Was due to the characteristics of the vcomplex-forming agents whereby under aI given set of operating conditions certain classes or compounds formed complexes with the agents present. Thus, if both isoparafns and naphtheneswere present in a mixture of hydrocarbone, the treatment of such a Amixture with thiourea resulted in the formation of complexes or both of these types of hydrocarbons with thiourea. For'many purposes the presence of onevor another type of compound invadmixture with other' types is undesirable.V If, for example this process Were being used' for the preparation of highl octane gasoline, the presence of naph-thenes in the product would be undesirable. Therefore, `an improvement upon the known process Would Vcomprise av revision thereof whereby the nal product substantially excluded naphthenes and largely comprised isoparafns..

In a number of instances a mixture of organic 'compounds contains a relatively minorY fraction of material which will form crystalline complexes with one of the above agents. It has been noted that if only a minor amount or complexes are formed and thereafter separated from. the mix ture by ltrationl the layer of crystals tends to forfm a dense' layer which clogs" the lter' cloth l and thus reduces 'the eieie'ncy or the nltration either urea or thoure'a. Itis another object or this invention to providev for thev production or more highly fractionated materials than those hereto'forev possible by 'the sut-ject extractive fracobjects will become apparent during the following discussion.

Now, in accordance with this invention, it has been found that the fractionation of mixtures of organic compounds by the subject extractive fractionation processes may be improved by recycling part of the complexes back to the mixture prior to the separation step. By part of the complexes is meant a portion of the organic compounds extractively fractionated from the original mixtures, either in the form of the unaltered complex or in its regenerated form free of any complex-forming agent. Still in accordance with this invention, it has been found that the efficiency of separating complexes from their mixtures with other compounds may be raised by the step described above. Again in accordance with the present invention, it has been found that the feed may be enriched in a desired fraction by employing the above step as more fully described hereinafter.

In carrying out the process of the present in- Vention, mixtures of organic compounds are con*- tacted with a complex-forming agent (suitably either urea or thiourea) and passed to a separator wherein the complexes are separated from the rainate. By ranate is meant that portion of the original mixture which fails to form complexes with the agent present under the conditions employed. Following isolation of the complexes, the process according to the present invention comprises two alternative steps: the complexes may be passed to a regenerator or part of the complexes may be recycled to the mixer and the remainder sent to the regenerator. mixer is meant that apparatus wherein the mixture of organic compounds is contacted with a complex-forming agent. If the latter alternative is employed the fraction to be returned to the mixer is predetermined by the conditions which it is desired to maintain in the mixture as well as by the desired composition of the nal product. The complexes may be fractionated into any type of desired fractions, either according to molecular weight, chemical type, structural type, solubility, etc. The fractionation may be conducted by fractional crystallization from a lean solvent wherein only one part of the complexes will dissolve while the remainder are unaffected. Alternatively, the complexes may be fractionated by melting point, the temperature being raised until a particular fraction of the complexes are liquid and the remainder are unaffected at which Ypoint one phase or the other is recycled to the mixer. Other types of fractionating the complexes will be more or less obvious to those familiar with the art of fractionation.

The fraction of the complexes returned to the mixer enrich the feed in regard to that particular type of organic compound returned in complex form. Thus, the total amount of complexes separated thereafter from the enriched feed will be altered to the extent of this addition. This recycling of a fraction of the complexes may be conducted to the point at which the complexes finally separated have a desired composition. From the standpoint of eiciency this should be effected in a minimum number of recycling operations. By the addition of complexes to the mixer a heavier cake of crystals can be built up on the filter (if such is the separating means). It has been found that a relatively thick cake of such crystals is structurally more porous than a thin densely formed layer such as is obtained when the original mixture contains only a small amount of complex-forming .organic compounds.

At times it is undesirable to fractionate the complexes as described above. For example, some of said complexes are relatively unstable and tend to decompose if heated to any appreciable extent, or have substantially the same solubility throughout, thus prohibiting fractional crystallization. Under such circumstances the total amount of complexes may be passed directly from the sep arator to a regenerator wherein the complexforming agent and the organic compounds in complex form therewith are separated in such a was7 as to recover the agent in its original form and separately recover the organic compounds extended therewith. The conditions of regeneration allow a second step at which fractionation may be conducted whereby part of the product is recycled to the feed and part is sent to its nal destination. For example, one means of regenerating organic compounds from their complexes comprises simple distillation, whereby the complex decomposes and at least part of the organic compounds are distilled leaving residual compounds and complex-forming agents behind. It will be readily appreciated that the conditions of distillation may be adjusted to the point that a fraction of a desired boiling range may be recovered either as a distillate or as a bottoms from a distillation step. Other means of regeneration are more fully described hereinafter at which point other types of fractionation of the products recovered will be described.

The fraction of the regenerated compounds recycled to the feed enriches the latter in that particular type of compound. Since the material returned to the feed is of a type which will form a complex with the agents employed, a suiiicient amount of such agents must be possible to form complexes not only with the active material already in the feed but also with the recycled compounds. It is undesirable to recycle at this stage if the fractionation as described hereinabove can be effectively conducted. This is due to the fact that it is necessary to form and regenerate complexes more than once thus, decreasing the eiliciency of the operation. However, if the regenerated compounds can be fractionated in a particular way to arrive at a desired fraction more effectively than when in complex form, then such multiple complex formation and regeneration becomes necessary.

By way of illustration, reference may be made to the drawing which comprises a flow diagram for the fractional extraction of mixtures of organic compounds in accordance with the method of the present invention. For this illustration a mixture of petroleum hydrocarbons comprises isoparafiins, normal paraflins, and naphthenes which would be contacted with thiourea. The mixture of hydrocarbons and a saturated alcoholic solution of thiourea are introduced to a mixer I at room temperature. The mixture 1s stirred for a short length of time to permit maximum contact of the thiourea solution with the hydrocarbons. Crystalline complexes form between thiourea and the hydrocarbons of naphthenic and isoparaifmic structure. The total mixture is Sent to a separator 2, wherein the rainate is ltered away from the crystalline complexes. A nal product is desired which is to be a mixture of naphthenes and isoparaflins having a minimum boiling point of about C. The mixture of complexes separated as described above is too unstable to fractionate by distillation. Therefore, it is sent directly from the separator 2 to the regenerator 4 wherein the comasiasva plexes are heated to their decomposition temperature and are fractionally distilled, the temy perature of distillation being adjusted to the point whereat the hydrocarbons which distill have boiling points below the minimum desired final product. The bottoms from this distillation comprise isoparafin and naphthenic hydrocarbons having a minimum boiling point of the desired range in admixture with regenerated thiourea. 'Ihe latter separates from the hydrof carbons and may be recycled for further complex formation. In order to enrich the original feed stock in the desired isoparain and naphthene fraction, part of the latter regenerated hydrocarbons are recycled to the mixer l while the remainder is passed to storage. By recycling this fraction to the mixer the feed is enriched in the type of hydrocarbon having thev predetermined boiling range thereafter the complex for mation and separation are conducted as described above. The separation step constituted the formation of a relatively heavy lter cake of crystalline complexes which was highly porous and allowed faster liltration than was possible during the initial separation described above.

The mixtures of organic compounds which may be treated with urea by the process of the present invention comprise compounds having substantially normal structure and/or compounds having a predominating substituent of substantially normal structure. Conditions may be employed whereby certain normal organic compounds are separated from other normal organic compounds, or from the other organic compounds such as isoparaiiins, aromatics, naphthenes, etc. The organic compounds of normal structure which may be formed intocomplexes by the process of the present invention include both saturated and unsaturated compounds, especially the parains, and olens. The normal compounds may be of a number of types, such as hydrocarbons, alcohols, ketones, aldehydes, esters, amines, amides,

suldes, disuldes, mercaptans, acids, halogenat.-

ed compounds, ethers, nitro-compounds, silicones, carbohydrates, etc. The hydrocarbons respond especially well' to the process of the presentinvention.

Suitable hydrocarbons which form crystallineY complexes with urea include the paraiiinic hy'- drocarbons such as; butano, pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane,Y tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane, eicosane, etc;

Olen hydrocarbons which may be treated by the process of the present invention include l-butene, 2-butene, l-pentene, 2pentene, l-hexene, Z-hexene, 3-hexene, 1-heptene, Z-heptene, 3heptene, l-octene, 2-octene, 3-octene, 4-octene, 2nonene, 3-nonene, 4-nonene, 1-decene, 2-decene, 3-decene, 5-decene, 1-undecene, 2-undecene, 5undecene, 1-dodecene6dodecene, l-tridecene, G-tridecene, 1pentadecene, 8-heptadecene, 13- heptacosene, etc.

VAnother class of hydrocarbons which may be formed into complexes with urea, according to the process of the present invention are the normal oliolelins such as 1,2-butadiene, 1,3- butadiene, 1,2-pentadiene, 1,3-pentadiene, 1,4- pentadiene, 1,2-hexadiene, 1,3-hexadiene, 1,4- hexadiene, 1,5 -hexadiene, 2,3 -hexadiene, 2,4- hexadiene, 1,3-heptadiene, 1,6-heptadiene, 2,4- heptadiene, 1,4 octadiene, 1,5'- octad'iene, 1,7- octadiene, 2,6.-octadiene,3,5foctadiene, L-none ad'iene, L-nonadiene, 2,6-nonadiene, 1,3-d'eca- 6 diene, 1,4-decadiene, 1,9decadiene, f-checadi` ene, 3,7-decadiene, 2,6-dodecadiene, 12,17-octadecadiene, etc.

Normal hydrocarbons of a greater degree of unsaturation which form crystalline complexes with urea by the process or the present invention include the trioleiines,v acetylenes, diacetyl enes, oleiin-acetylenes and the dioleiin-acetyl* enes, I including 1,3,5 hexatriene, 1,3,5 e heptatriene, 2,3,6-octatriene, ethylacetylene', propyl-4 acetylene, butylacetylene, amylacetylene, caprylidene, 4-octyne, diacetyl'ene, propyl-dacety-lene,

Normal alcohols, especially those having six or more carbon atoms, may be treated by theJ present process to form complexes with urea.' These include the aliphatic monohydric alcohols' such as hexyl alcohol, heptyl alcohol, octyl alcohol, nonyl alcohol, decyl alcohol, dodecyl alcohol, cetyl alcohol, carnaubyl alcohol, and the polyhydric alcohols, such as ethylene glycol', diethylene glycol, propylene glycol and hexitol.

Ethers of normal structure forming complexes with urea include acetal, dioxane, paraldehyde, crotonyl ether,A etc. Aldehydes of normal structure also respond' to the process oi this invention, including butyraldehyde, valeraldehyde, caproaldehyde, palmitic aldehyde, citral adipaldehyde, etc. Ketones which form urea complexes are exemplified by 3-hexanone, palmitone, 2,3' pentanedione, etc. Acids also may be treated according to the subject process. Typical. normal acids forming urea complexes are the nor-v mal fatty acids, especially those having four or more carbon atoms, such as butyric; valerio; caproic, enanthylic, capryli'c, pela'rgonic, capric," undecylic, lauric,A tridecoic, myristic, pentad'e'canoie, palmitic, margaric, stearic, etc., acid. Acrylic acidsV also respond, su'ch as methylacrylic' acid, tiglic acid, oleic acid, etc. The acetylene acids form urea complexes. These. include sorbicand Linoleic acids.

Other types of normal-structured compounds which. may be treated. according to the' process of the present invention include esters, such as: amyl acetate, ethyl steal-ate,y etc; amines such' as nedecyl amine.v dbutyl amine and triethyl amine.; amid'es, such as stea'rarnide;` mercapta'ns, such as heptyl mercaptan; and other organic compounds. of normal structure, including halot geriated derivatives of the above compounds, thioalcohols, alkyl hydrazines, thioaldehydea amino acids, nitroparaflins, etc.

The mixtures containing the organic conipounds of normal structure maybe composed vsolely of mixed normal compounds, or they may contain, materials substantially inert. toward urea, such as branched parains, isoclens, arc-V m-atics, cycloparains, etc. Usually, especially Y whenv treating natural products such as petroganic com-pounds in order to modify theV type and degree oi crystallization of the latter with urea. The reasonory and use of' diluents is discussed hereinafter. A

Hydrocarbons which form complexes with thioureaare those having a pre'dominating member which is' a substantially branched radical or a naphthene radical, such as alkaryl hydrocarbons wherein at least one alkyl group is an isoparain radical of about six or more carbon atoms.

Isoparaflins which form complexes with thiourea include isobutane, isopentane, 2,2- dimethylpropane, isohexane, 2,3-dimethylbutane, 2- methylpentane, 3-methylpentane, Z-ethylbutane, 2 ethylpropane, 1,1 dimethylpentane, 1,2 dimethylpentane, 1,3 dimethylpentane, 1,4 dimethylpentane, Z-ethylpentane, B-ethylpentane, 2npropylbutane, 2-isopropylbutane, 2-methylhexane, 3methylhexane, 2,2-dimethylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane, 3,3- dimethylpentane, 2,2,3-trimethylbutane, Z-methylheptane, B-methylheptane, 4-methylheptane, 3-ethy1hexane, 2,2-dimethylhexane, 2,3-dimethhexane, 2,4-dimethylhexane, 2,5-dimethylhexane, 3,3-dimethylhexane, 3,4-dimethylhexane, 2,2,3- trimethylpentane, 2,2,4-trimethylpentane, 2,3,3- trimethylpentane, 2,3,4-trimethylpentane, 223,3- tetramethylbutane, Z-methyl-S-ethylpentane, 3- methyl-S-ethylpentane, 2-methyloctane, B-methyloctane, 4methyloctane, 2,2-dimethylheptane, 2,3-dimethylheptane, 2,4-dimethylheptane, 2,5- dimethylheptane, 2,6-dimethylheptane, 3,3-dimethylheptane, 3,4-dimethylheptane, 3-ethy1- heptane, 4ethylheptane, 2,2,3-trimethylhexane, 2,2,4 trirnethylhexane, 2,2,5 trimethylhexane, 2,3,3 trimethylhefxane, 2,3,5 trimethylhexane, 2,4,4-trimethy1hexane, 3,3,4-trimethylhexane, 2- methyl-S-ethylhexane, 2-methyl-4-ethylhexane, 2,2,3,3-tetramethylpentane, 3,3-diethylpentane, 2,2 dimethyl 3 ethylpentane, 2,3 dimethyl -ethylpentane, 2,4 dimethyl- 3 ethylpentane, 2,2,3,4tetramethylpentane, 2-methylnonane, 3- methylnonane, 4 methylnonane, 5 methylno nane, 2,2 dimethyloctane, 2,3 dimethyloctane, 2,4-dimethyloctane, 2,5-dimethyloctane, 2,6-dimethyloctane, 2,7-dimethyloctane, 3,3-dimethyloctane, 3,4-dimethyloctane, 3,6-dimethyloctane, 4,5-dimethyloctane, S-ethyloctane, 2,2,3-trirnethylheptane, 2,3,3-trimethylheptane, 2,2,6-trimethylheptane, 2,3,6-trimethy1heptane, 2,4,4-trimethylheptane, 2,4,6-trimethylheptane, 3,3,5-trimethylheptane, S-methyl-S-ethylheptane, 4-propylheptane, 4-isopropylheptane, 2,2,3,3tetrameth ylhexane, 2,2,3,4tetramethylhexane, 2,2,5,5tetramethylhexane, 2,2-dimethyl 4 ethylhexane, 3,3,4,4 tetramethylhexane, 3,3 diethylhexane, 3,4 diethylhexane, 2,2,4 trimethylheptane, 2,2,4,5-tetramethylhexane, 2-methyl-5-ethylheptane, 4-methyldecane, -methyldecane, 2,3-dimethylnonane, 2,4-dimethy1nonane, 2,5-dimethylnonane, 2,6-dimethylnonane, 3,3-dimethylnonane, 4-ethy1nonane, 5-ethylnonane, 2,3,7-trimethyloctane, 2,4,7-trimethy1octane, 2,2,3,3tet ramethylheptane, 2,2,4-trimethyloctane, 2,2,4,6 tetramethylheptane, 2,2,4,5-tetramethylheptane, 3 methylundecane, 4 methylundecane, 2,3 dimethyldecane, 2,5-dimethy1decane, 2,6-dimethyldecane, 2,9-dimethyldecane, S-ethyldecane, 5- propylnonane, 2,2,'7,7-tetramethyloctane, 2,3,6,"I tetramethyloctane, 2,4,5,7 tetramethyloctane, 3,3,6,6-tetramethy1octane, 2-methyl-5-propy1octane, 3,6-diethyloctane, 2,6-dimethy1-3-isopropylheptane, 4,5 diethyloctane, 2,2,4,6,6 pentamethylheptane, 2,2,4,4,6-pentamethylheptane, 5- methyldodecane, 2,10 dimethylundecane, 2,5,9- trimethyldecane, 4-pi'opyldecane, 4-ethy1undecane, -butylnonane, 2,11-dimethyldodecane, 4,5- diisopropyloctane, 2,7 dimethyl-4,5-diethyloctane, 4-propylundecane, 2,7-di1nethyl-4-isobutyloctane, 2,6,l-trimethyldodecane, 2,6,11-trirnethyldodecane, 6-methyl-7-ethyldodecane, 5-propyldodecane, 6-propyldodecane, 4-methy1-6-propylundecane, 6,9-dimethyltetradecane, 7,8-dimethyltetradecane, 3 ethyltetradecane, 5,7 diethyldodecane, 2,6,7,1l-tetramethyldodecane, 4,7-dipropyldecane, 2,2,3,3,6,6,7,7 octamethyloctane, 3,12-diethyltetradecane, 2,6,11-trimethyl-9-isobutyldodecane, 2,6 dimethyloctadecane, 5,7,9 triethyltetradecane, 2-methyl-4-isobutylhexadecane, 2,9dimethyl-5,6diisoamyldecane, 4,8,13,17 tetramethylicosane, 2,11-dimethyl-5,8diisoamyl dodecane, lll-nonyl-nonadecane, 2,6,10,14,18,22 hexamethyltetracosane, 2,6,12,16tetramethyl-9 (2,6-dimethyloctyl) heptadecane, etc.

As stated hereinbefore another type of hydrocarbon which readily forms complexes with thiourea is that of the naphthenes. Typical species of this group include cyclopropane, methylcyclopropane, 1,1 dimethylcyclopropane, 1,2 dimethylpropane, ethylcyclopropane, 1,1,2- trimethylcyclopropane, 1,2,3 trimethylcyclopropane, l-methyl-Z-ethylcyclopropane, propylcyclopropane, 1-methy1-2-propylcyclopropane, cyclobutane, methylcyclobutane, ethylcyclobutane, 1,2-dimethylcyc1obutane, propylcyclobutane, isopropylcyclobutane, 1,2 diisopropylcyclobutane, 1,2 dimethyl 3,4 diethylcyclobutane, 1,1,2,2 tetramethyl 3,4 diisopropylcyclobutane, cyclopentane, methylcyclopentane, 1,1-dimethylcyclopentane, 1,Z-dimethylcyclopentane, 1,3-dimethylcyclopentane, ethylcyclopentane, propylcyclopentane, isopropylcyclopentane, 1,1,3-trimethylcyclopentane, 1-rnethyl-2-ethylcyc1opentane, 1- methyl-S-ethylcyclopentane, butylcyclopentane, isobutylcyclopentane, 1 methyl 2 propylcyclopentane, 1-methyl-S-propylcyclopentane, 1,3- dimethyl 2 ethylcyclopentane, 1,3 dimethyl- 5 ethylcyclopentane, 1,1 diethylcyclopentane, amylcyclopentane, isoamylcyclopentane, 2-cyclopentylpentane, 1-methyl-B-butylcyclopentane, 1- methyl-2,5-diethy1cyclopentane, 1,2,3-trimethy1- 4-isopropylcyclopentane, heptycyclopentane, cyclohexane, methylcyclohexane, ethylcyclohexane, 1,1-dimethy1cyclohexane, 1,2-dimethy1cyclohexane, 1,3-dimethylcyclohexane, 1,2,3-trimethylcyclohexane, 1,3,5-trirnethylcyclohexane, butylcyclohexane,v 1 methyl 4 ethylcyclohexane, 1-methyl-3-propylcyclohexane, l-methyl-B-isopropylcyclohexane, 1,3 dimethyl 5 ethylcyclohexane, 1,3 diethylcyclohexane, amylcyclohexane, pentamethylcyclohexane, 1,2-dimethyl- 3,6diethylcyclohexane, 4-cyc1ohexy1heptane, 3- cyclohexyl-3ethylpentane, triisopropylcyclohexane, 2,8-dimethyl-5-ethyl-5-cyc1ohexylnonane, 1- methyl-4-isopropyl-2-dodecyclohexane, octadecyclohexane, propylcycloheptane, etc.

The ratio of theA complex-forming agent to active organic compounds will Vary with the type of mixture toV be treated and with the conditions of complex formation. For example, the extractive fractionation may be carried out With the intention of removing from the mixture the maximum amount possible of the compounds of normal structures present. In this particular case, it is preferred practice to Contact the mixture with urea employed in an amount in excess of that necessary for complete complex formation.

Complexes may be formed having varying amounts of the complex-forming agent combined with the active organic compound. When the temperature or other conditions during complex formation are such that about 3 mols of the agent combined with about every 4 carbon atoms of the active organic compound, it is preferred prac- 9 tice to contact the active organic compound with an amount of the agent somewhat inexcess of this ratio.

The formation, separation and purification of the complexes having been accomplished as described hereinbefore, there remains the step of decomposing the complexes in order to recover the active organic compounds present therein. While a number of methods have been `found for effecting such Ia decomposition or regeneration, the following methods have been found to be the most ysatisfactory for use when carrying out the process of the present invention:

A. Simple distillation.

B. Steam distillation. v Y C, Application of a solvent forv the co forming agent.

D. Heating.

E. Application of a solvent for a, particular fraction of the regenerated organic compounds.

v The complexes, `as has been pointed out hereinbefore, are relatively unstable formations which appear to be loose combinations involving hydrogen .bonding or some form of molecular attraction, the exact nature of. which has not been deduced. It has been found that due to their unstable character, splitting into the component parts of the complex may be readilyV accomplished, the complex-forming agent and the organic compounds inv complex combination therewith separately Vrecovered in their original state.

By subjectingy the complexes to distillation simultaneous destruction of the complex and fractionation of the organic compounds regenerated therefrom may be accomplished. The distillation may take place under normal or reduced pressures and the temperature and pressure are so adjusted that the complexes are readily destroyed and the compounds regenerated therefrom are distilled into fractions which can be utilized for the purposesconside'red herein'. For example, if it is desired to enrich the feed with low boiling normal hydrocarbons, complexes of ureaand a mixture of normal hydrocarbons may be'dec'omposed by distillation and the distillan't maybe recycled to the mixer.

Steam distillation is a refinement of the above process and the principle of regeneration and fractionation applies here as well. Steam distillation is preferable where the organic compounds to be regenerated are of such high boiling point that their distillation would be accomplished by substantial decomposition.

A further type of regeneration comprises addition of a solvent for the complex-forming agent such as water or alcohol to the complex and the application of heat to facilitate the regeneration. By this means the regenerated organic compounds separate from the solution of the complex-forming agent and subsequently may be fractionated by normal purification or fractionation procedures.

A more preferred type of regeneration comprises the addition of a solvent for one or more fractions of the organic compounds to be regenerated from the complexes. When such a mixture is heated the complex decomposes, thus regenerating the organic compounds and complex-forming agents and, in presence of such a solvent, a solution of part of the regenerated organic compounds which form and may be readily separated from the insoluble fractions which are present. Hence, fractionation according to solubility may be readily accomplished.

Fractionation by simple heating is satisfactory plex- 10 for some purposes. Following the regeneration by such means it is usually necessary to purify or fractionate thev regeneratedcompounds and the regenerated complex-forming agent for further use.

The process of the present invention is .useful for the preparation of high octane gasoline or of high Diesel index fuel as well as for the preparation of internal combustion engine fuels having a narrow boiling range.

I claim as my invention:

1. In the process of fraotionating a mixture of organic compounds, said mixture containing a fraction A comprising substantially straightchain materials and a fraction B comprising predominantly non-straight-chain materials, wherein said. mixture is treated with urea and the crystalline complexes which form between urea and at least part. of fraction A are separated from fraction B, said treatment being conducted below the decomposition temperatures of said complexes, the improvement which comprises recycling at least part of they fraction A thusr separated to enrich additional amounts of the original mixture prior to its/treatment with urea, forming crystalline complexes by treatment of the enriched mixture with urea and separating said complexes from unreacted? material by filtration, said enriched mixture of complexes forming. a more porous filter cake.

l2. In a process forA the fractionation of a mixture ofy petroleum hydrocarbons, said mixture containing a fraction Acomprising substantially straight-chain hydrocarbons,v and a fraction B comprising non-straight-chain hydrocarbons, wherein said mixture is treated with ureaand the crystalline complexes so formed between fraction A hydrocarbons and urea are separated from fractionB, said treatment. being conducted below the decomposition temperatures of said complexes, the improvement which comprises. recycling atleast part of the complexes of fraction A to enrich .additional quantities. of the original mixture prior to the ,urea treatment, forming crystalline complexes by ktreatinent' ofthe enriched mixture with urea and Iseparating said compleXes from unreacted material by filtration, said enriched mixture of complexes forming a more porous filter cake.

3. In a process for the fractionation of a mixture of organic compounds, said mixture containing a fraction A comprising branched-chain compounds and a fraction B comprising straightchain compounds, wherein said mixture is treated with thiourea, and the crystalline complexes so formed between fraction A compounds and thiourea are separated from fraction B, said treatment being conducted below the decomposition temperatures of said complexes, the improvement which comprises recycling at least part of fraction A thus separated to enrich additional amounts of the original mixture 'prior to treatment with thiourea forming crystalline complexes by treatment of the enriched mixture with thiourea and separating said complexes from unreacted material by filtration, said enriched mixture of complexes forming a more porous filter cake.

4. In a process for the fractionation of a mixture of petroleum hydrocarbons, said mixture containing a Vfraction A comprising isoparaiiins and naphthenes, and a fraction B comprising substantially unbranched hydrocarbons, wherein said mixture is treated with thiourea and the crystalline complexes so formed between thiourea and andere l1 fraction A hydrocarbons are separated from fraction B, said treatment being conducted below the decomposition temperatures of said complexes, the improvement which comprises recycling at least part of fraction A thus separated to enrich additional amounts of the original mixture prior to treatment with thiourea forming crystalline complexes by treatment of the enriched mixture with thiourea and separating said complexes from unreacted material by filtration, said enriched mixture of complexes forming a more porous iilter cake.

5. In a process for the fractionation of a mixture of organic compounds by treatment with a complex-forming agent of the group consisting of urea and thiourea, said mixture comprising a fraction A containing compounds capable of forming crystalline complexes with the agent and a fraction B containing compounds incapable of a complex formation with said agent, wherein crystalline complexes of the agent and at least a part of fraction A are formed by treating the mixture with the agent below the decomposition temperatures of said complexes, the improvement Which comprises recycling at least part of said complexes to enrich additional amounts of the original mixture prior to treatment with the agent, forming crystalline complexes by treatment of the enriched mixture with the complexforming agent and separating said complexes from unreacted material by ltration, said enriched mixture of complexes forming a more porous filter cake.

6. In a process for the fractionation of a mixture of organic compounds by treatment with a complex-forming agent of the group consisting of urea and thiourea, said mixture comprising a fraction A containing organic compounds capable of forming crystalline complexes with the agent and a fraction B containing organic compounds incapable of complex formation with said agent, wherein crystalline complexes of the agent and at least a part of fraction A are formed by treating the mixture with the agent below the decomposition temperatures of said complexes, the improvement which comprises recycling at least part of fraction A thus separated to enrichwadditional amounts of the original mixture prior to treatment with the agent, forming complexes by treatment of the enriched mixture unreacted material by filtration, said enriched mixture of complexes forming a more porous ilter cake.

'7. In a process for the fractionation of a mixture of hydrocarbons by treatment with a complex-forming agent of the group consisting of urea and thiourea, said mixture comprising a fraction A containing hydrocarbons capable of forming crystalline complexes with the agent and a fraction B containing hydrocarbons incapable of complex formation with said agent, wherein crystalline complexes of the agent and at least a part of fraction A are formed by treating the mixture with the agent below the decomposition temperatures of said complexes, the improvement which comprises recycling at least part of fraction A thus separated to enrich additional amounts of the original mixture prior to treatment with the agent, forming complexes by treatment of the enriched mixture unreacted material by iiltration, said enriched mixture of complexes forming a more porous filter cake.

LLOYD C. FETIERLY.

REFERENCES CITED FOREIGN PATENTS Country Date Great Britain Jan. 23. 1937 OTHER REFERENCES Walton et al.: Jour. Am. ChemiScc., Vol. 47, 320-5 (1925). v A Bengen: Tech. Oil Mission, Reel 143, 1946.

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1. IN THE PROCESS OF FRACTIONATING A MIXTURE OF ORGANIC COMPOUNDS, SAID MIXTURE CONTAINING A FRACTION A COMPRISING SUBSTANTIALLY STRAIGHCHAIN MATERIALS AND A FRACTION B COMPRISING PREDOMINANTLY NON-STRAIGHT-CHAIN MATERIALS, WHEREIN SAID MIXTURE IS TREATED WITH UREA AND THE CRYSTALLINE COMPLEXES WHICH FORM BETWEEN UREA AND AT LEAST PART OF FRACTION A ARE SEPARATED FROM FRACTION B, SAID TREATMENT BEING CONDUCTED BELOW THE DECOMPOSITION TEMPERATURES OF SAID COMPLEXES, THE IMPROVEMENT WHICH COMPRISES RECYCLING AT LEAST PART OF THE FRACTION A THUS SEPARATED TO ENRICH ADDITIONAL AMOUNTS OF THE ORIGINAL 